The new tool, which users must enable in Gmail Labs to work (go to Settings > Labs > enable Apps Search), changes the "Search Mail" function in your Gmail account to "Search Mail and Docs." When you use the search function within your email, search results will include both email (like you're used to now) and document results, including attachments and Google Docs files. For now, email results show up first and faster than attachments, so if you choose to enable this lab, it won't slow down your search results.